linux-kernel - RE: [PATCH 03/36] memcg: adjust to support new THP refcounting

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Date:	Tue, 14 Jul 2015 16:58:42 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: RE: [PATCH 03/36] memcg: adjust to support new THP refcounting

Kirill A. Shutemov wrote:
> As with rmap, with new refcounting we cannot rely on PageTransHuge() to
> check if we need to charge size of huge page form the cgroup. We need to
> get information from caller to know whether it was mapped with PMD or
> PTE.
> 
> We do uncharge when last reference on the page gone. At that point if we
> see PageTransHuge() it means we need to unchange whole huge page.
> 
> The tricky part is partial unmap -- when we try to unmap part of huge
> page. We don't do a special handing of this situation, meaning we don't
> uncharge the part of huge page unless last user is gone or
> split_huge_page() is triggered. In case of cgroup memory pressure
> happens the partial unmapped page will be split through shrinker. This
> should be good enough.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

checkpatch fixlet:

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6dd365d1c488..117bedd02db2 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1103,8 +1103,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	if (unlikely(!page))
 		return -ENOMEM;
 
-	if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, &memcg, false))
-	{
+	if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
+				&memcg, false)) {
 		ret = -ENOMEM;
 		goto out_nolock;
 	}
--
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